Introduction • Brain of the computer • silicon chip that contains a CPU • First microprocessors emerged in the early 1970. • A microprocessor is designed to perform arithmetic and logic operations. • It is the most expensive component found inside the system. • Intel is world leader in Microprocessor.

Definition • A microprocessor may be briefly defined as a (VLSI) chip that performs a task of the central processing unit of a microcomputer or other automatic control systems.

Definition (2) • Microprocessor is multipurpose, programmable logic device that reads the binary instruction from storage device called memory, accepts the binary data as input and processes data according to those instructions, and provides the results as output.

• Microprocessor is broadly divided into three parts. • Arithmetic logic Unit : – Arithmetic logic unit, the part of a computer that performs all arithmetic computations, such as addition and multiplication, and all comparison operations. The ALU is one component of the CPU . • Registers: – A register is one of a small set of data holding places that are part of a computer processor . A register may hold a computer instruction , a storage address, or any kind of data. • Control Unit : – The control unit is the circuitry that controls the flow of information through the processor, and coordinates the activities of the other units within it.

• Control lines: communicate with ALU and memory by generating control signals, e.g – R/W lines – I/O lines – interrupt lines. • Internal registers: Registers work under the direction of the control unit to accept, hold, and transfer instructions or data and perform arithmetic or logical comparisons at high speed. Few of the registers are : – Program counter – Accumulator – Flag register – General purpose register – Stack pointer

What to study • when learning about a new microprocessor , one must study the following: – Microprocessor architecture – Pin functions – Control signals – Addressing modes – Instruction set • The Mp we will discuss : – 8085 – 8086 – 6800 – 6502 and many other acc. To availability of time 

The 8085 Microprocessor

8085 INTRODUCTION The features of INTEL 8085 are : • It is an 8 bit processor. • It is a single chip N-MOS device with 40 pins. • It has multiplexed address and data bus.(AD0-AD7). • It works on 5 Volt dc power supply. • The maximum clock frequency is 3 MHz while minimum frequency is 500kHz. • It provides 74 instructions with 5 different addressing modes.

• It has 40 pins and uses +5V for power. It can run at a maximum frequency of 3 MHz. • The pins on the chip can be grouped into 6 groups: 1. Power supply and frequency. 2. Serial I/O ports. 3. Address Bus. 4. Data Bus. 5. Control and Status Signals. 6. Externally Initiated Signals. www.yesnarayanan.blogspot.com

Power supply and Frequency signals • The microprocessor operates on a singles +5V power supply connected to Vcc at pin number 40. • The ground is connected to Vss at pin number 20. • There are 3 pin in the frequency control group 1. X1 2. X2. 3. CLK OUT. (i) X1&X2: Pin number 1&2 are the inputs from the clock generating circuit. It is use to synchronize the operations of the 8085 microprocessor. • The microprocessor has operates at 3MHz frequency. (ii) CLK OUT: Pin number 37, It is an output pin. This signal is generated by microprocessor. It can be used as the system clock for other devices.

Clock circuit www.yesnarayanan.blogspot.com

Serial I/O ports • These signals are used for giving serial input and output data. • There are used two pin for serial I/O data . 1. SID: Serial Input Data. Pin number 5 This pin provides serial input data. The serial data on this pin is loaded into the seventh bit of the accumulator. 2. SOD: Serial Out Data Pin number 4 This pin provides the serial output data. The serial data on this pin delivers its output from the seventh bit of the accumulator. www.yesnarayanan.blogspot.com

Address Bus and Data Bus • 8085 μp consists of 16 signal pins use as address bus. • Address bus is available from pin number 21 to 28. • Divide into 2 part: A15 – A8 (upper) and AD7 – AD0 (lower). – A15 – A8 : Unidirectional, known as ‘high order address’ bits. – AD7 – AD0 : bidirectional and dual purpose pins also known as ‘low order address’ bits. – To execute an instruction, at early stage AD7 – AD0 uses as address bus and alternately as data bus for the next cycle. – The method to change from address bus to data bus known as ‘bus multiplexingbus multiplexing’.

• The 8 address bits are multiplexed (time shared) with the 8 data bits. AD0 to AD7 • Pin number 12 to 19 are used for data bus in microprocessor. • The data bus is a bidirectional bus. The data bus can transfer the data from CPU to memory or vice versa. The data bus also connects the I/O ports and microprocessor.

Control and Status Signals • There are 4 main control and status signals. 1. ALE: Address Latch Enable: Pin number 30. • This signal is a pulse that become 1 when the AD0 – AD7 lines have an address on them. It becomes 0 after that. • This signal can be used to enable a latch to save the address bits from the AD lines.

2. RD: Read. Active low • Pin number 32 • The read control signal is used to control the reading operations of microprocessor. • indicate that the I/O or memory selected is to be read and data are available on the bus.

3. WR: Write. Active low. • Pin number 31 • The write control signal is same as read signal. • Indicate that the data available on the bus are to be written to memory or I/O ports. www.yesnarayanan.blogspot.com

• S1 and S0: • Pin number 33&29 • S1 & S0 are two status signals. • These signals are used to indicate the internal operation of microprocessor. • Status signals to specify the kind of operation being performed . www.yesnarayanan.blogspot.com

1. RESET • RESET IN: This is an input signal. Pin number-36 • When the signal on this chip goes low, the program counter is set to zero. • RESET OUT: Pin number-3 • This signal is generated by microprocessor in response of the signal RESET IN when RESET IN is logic 0, RESET OUT is logic 1,This signal show that microprocessor in reset. www.yesnarayanan.blogspot.com

2. READY • Pin number-35 • If Ready is high during a read or write cycle, it show that the memory or peripheral is ready to send or receiving the data. • If Ready is low, the CPU wait for Ready to go high before completing the read or write cycle. • A peripheral may be a LCD display or analog to digital converter or any other. These peripherals are connected to microprocessor using the READY pin. If READY is high then the peripheral is ready for data transfer.

• HOLD: • This indicates if any other device is requesting the use of address and data bus. Consider two peripheral devices. One is the LCD and the other Analog to Digital converter. Suppose if analog to digital converter is using the address and data bus and if LCD requests the use of address and data bus by giving HOLD signal, then the microprocessor transfers the control to the LCD as soon as the current cycle is over. After the LCD process is over, the control is transferred back to analog and digital converter.

• DMA is a method of transferring data from the computer's RAM to another part of the computer without processing it using the CPU. • DMA can save processing time and is a more efficient way to move data from the computer's memory to other devices. • In order for devices to use direct memory access, they must be assigned to a DMA channel. Each type of port on a computer has a set of DMA channels that can be assigned to each connected device. For example, a PCI controller and a hard drive controller each have their own set of DMA channels.

• HLDA: Pin number-38 • It is active high signal. • This signal acknowledges the HOLD request. • It’s inactive by the microprocessor after the I/O device has completed the DMA operation. www.yesnarayanan.blogspot.com

Applications of Microprocessors and Microcontrollers ...

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